This is what the FF person sent me:

I can reproduce the problem in a new profile. As far as I can tell, Firefox sends the identical information to the server: same referring page address, same cookies (of course, the session cookie itself and last visit time are different), on both my old profile and the new profile. That's why it's so puzzling that the server responds with a different page.
I don't see any progress toward a fix over on the My Little Forum forum, but it was just reported yesterday: http://mylittleforum.net/forum/index.php?mode=thread&id=8967
(This forum is open source, but trying to read PHP makes me soooo tired.)

Has anyone looked into this issue? Would really appreciate some feedback or is there another place to report bugs?